Notes In Genetics

Notes Genetics by R. P. Levine Published by Holt, Rinehart and Winston, Inc. : USA, 1962 Gene- genetic material can undergo some sort of change so that its action results in the production of altered phenoytpe. Mutation may arise spontaneously within “pure lines” of organisms. Definition: An event that gives rise to a heritable alteration in the genotype. In Drosophila melanogaster white-eye phenotype results from the inability of the organism to synthesize the red and brown eye pigments char. of wild-type flies.  Example of visible mutation Visible mutation – phenotypic effects of which the alterations is seen as an alteration in the organism’s morphology Ex. Dominant – Bar eye Recessive – White eye Visible mutations represent the loss of some essential function or structure Other mutations lead to the addition of structures or an extreme modification. Lethal mutations cause the death of the organism and many represent the loss or alteration of a function essential during embryonic development of the organisms. --Usually chromosomal mutations. Biochemical mutations represent the loss of a specific function (loss of ability to synthesize an essential metabolite) --Underlying cause of visible and lethal mutations Experiments in Genetics with Drosophila by Monroe W. Strickberger Published by John Wiley and Sons, Inc : New York, 1962 Localizing an Unknown Mutant -enables the prediction of mutan behavior in any crosses that are made, allows the comparison between mutants at similar loci and permits the establishment of useful multimutant stocks Recessive or Dominant • In the F1 of a cross between the mutant strain and almost any other stock which is wild type for that particular mutation o If F1 shows mutant phenotypeDominant o If NoneRecessive Sex Linked Recessive or Dominant

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If the cross between mutant females and males of a different stock produces an F1 where only the males are mutant, SEX-LINKED RECESSIVE o F1 females are consequently carrying 2 different parental X chromosomes which are free to cross over between the three different loci  If females permitted to mate with their brothers (cv and f) the F2 males will show the recombinant classes and provide linkage distances SEX-LINKED Dominant o Can be determined by crossing the males carrying the dominant to females of a different stock  Will only appear in females of this cross  F2 females will also show the recombinant classes

EFFECTS OF SINGLE MUTANTS Usually, occurrence of a change in a single phenotypic character Pleitropism- numerous phenotypic effects of a single gene